1. Field of the Invention
The invention relates to a technique for controlling a chopper circuit that uses soft switching operation.
2. Description of the Related Art
In the field using a semiconductor power converter, a soft switching chopper circuit is used in order to reduce a power loss. The chopper circuit includes a main circuit and an auxiliary circuit. The main circuit has a main reactor and a•main switching element. The auxiliary circuit has an auxiliary reactor, an auxiliary switching element and an auxiliary capacitor. In soft switching operation in which the auxiliary switching element is turned on and then the main switching element is turned on, there is known a technique described in Japanese Patent Application Publication No. 2008-283815 (JP-A-2008-283815) as a technique for controlling the timing of switching of the main switching element and the timing of switching of the auxiliary switching element.
In the above technique, when the electrical characteristic of a device that constitutes the chopper circuit (for example, the inductance of the auxiliary reactor, the capacitance of the capacitor, or the like) varies and differs from a rated value, switching of the main switching element may be performed in a state where the voltage between both ends of the main switching element is relatively high, so it has been pointed out that a large power loss occurs because of the switching.